Deck 44: Astrophysics and Cosmology

Question 1

Star A has twice the parallax as Star B. Star A is

A)twice as far as Star B.
B)four times as far as Star B.
C)eight times as far as Star B.
D)half as far as Star B.
E)one fourth as far as Star B.

Answer 1

half as far as Star B.

Question 2

Which is the latest stage (of those given below) in the evolution of a star?

A)red giant
B)white dwarf
C)protostar
D)geodesic
E)supernova

Answer 2

supernova

Question 3

One star has a surface temperature of 6000 K and another has a surface temperature of 7000 K. If the two stars have the same absolute luminosity, which star has the largest radius?

A)the star at 6000 K
B)the star at 7000 K
C)The two stars have the same radius.
D)Not enough information is given to determine.

Answer 3

the star at 6000 K

Question 4

Which of the following is arranged from hottest surface temperature to coolest surface temperature?

A)white dwarf, red giant, the sun
B)white dwarf, the sun, red giant
C)the sun, red giant, white dwarf
D)red giant, the sun, white dwarf
E)red giant, white dwarf, the sun

Question 5

Black holes

A)are holes in space, devoid of matter.
B)are predicted by Einstein's special theory of relativity.
C)are the collapsed remnant of stars.
D)cannot be detected in binary star systems.
E)are a violation of Einstein's general theory of relativity.

Question 6

The diameter of the Milky Way is 100,000 ly. This distance in SI units is

A)5 x 10¹⁵ m.
B)1 x 10²¹ m.
C)4 x 10³⁰ m.
D)3 x 10³⁶ m.
E)2 x 10⁴² m.

Question 7

The Chandrasekhar limit of stellar mass (below which a star will collapse into a white dwarf) is, if the mass of our Sun is M, about

A)0.8 M.
B)1.2 M.
C)1.4 M.
D)1.9 M.
E)2.8 M.

Question 8

A Hertzsprung-Russell diagram shows stars on a plot of

A)apparent brightness vs. temperature.
B)luminosity vs. temperature.
C)luminosity vs. distance.
D)magnitude vs. apparent brightness.
E)magnitude vs. distance.

Question 9

State Einstein's principle of equivalence.

Question 10

When a distant source emits light of a particular wavelength in the visible, and the source is moving away from us, the color of the light appears to us to be shifted toward the

A)red end of the visible spectrum.
B)blue end of the visible spectrum.

Question 11

In the standard model, about when after the Big Bang did the universe become transparent to radiation?

A)10^-43 s
B)10^-35 s
C)10³ s
D)3 × 10⁵ y
E)3 × 10⁶ y

Question 12

The Schwarzschild radius of a black hole is that radial distance from the center of a sphere within which not even light can escape. It was first discovered mathematically by Schwarzschild in 1916 after Einstein published his general relativity theory. It can be calculated from a star's mass M as: R = 2GM/c². Take the radius of both stars A and B as the Schwarzschild radius. If the mass of star A is twice as much as the mass of star B, the average density of star A, compared to star B will be

A)the same.
B)twice as much.
C)half as much.
D)four times as much.
E)one-fourth as much.

Question 13

Pulsars are rapidly spinning

A)regular stars like our Sun.
B)red giant stars.
C)neutron stars.
D)white dwarfs.
E)supernova.

Question 14

The appearance of the great range of brightness among stars is due to

A)the differences in the amount of light different stars emit.
B)the differences in the distances of stars from us.
C)both of the given answers
D)none of the given answers

Question 15

Supernovas are thought to always result in

A)neutron stars.
B)red giant stars.
C)regular stars like our Sun.
D)white dwarfs.
E)black dwarfs.

Question 16

If a galaxy is receding at 0.10 c, how far away is the galaxy if the Hubble parameter is 70 km/s/Mpc?

A)1.4 × 10⁹ ly
B)23 Mpc
C)76 Mly
D)7 Mpc
E)1.4 × 10⁷ ly

Question 17

A white dwarf star with a mass equal to that of the Sun is about the size of

A)the Sun.
B)the Earth.
C)a basketball.
D)a baseball.
E)a golfball.

Question 18

If a source of light is moving away at 10% the speed of light, its wavelength will

A)be lengthened by 22%.
B)be lengthened by 11%.
C)be shortened by 22%.
D)be shortened by 11%.
E)remain unchanged.

Question 19

Four different main-sequence stars are colored blue, orange, red, and yellow. What is their rank from coolest to hottest?

A)blue, yellow, orange, red
B)blue, orange, red, yellow
C)orange, blue, yellow, red
D)red, orange, yellow, blue
E)red, yellow, orange, blue

Question 20

The cosmic background radiation corresponds to a temperature of about

A)1.4 K.
B)2.7 K.
C)3.0 K.
D)3.3 K.
E)3.6 K.

Question 21

Estimate the speed of a galaxy that is 10 billion light-years away.

A)0.1c
B)0.3c
C)0.5c
D)0.7c
E)0.9c

Question 22

If the Hubble parameter is 25 km/s per million light years, how old is the universe?

A)10 × 10⁹ y
B)12 × 10⁹ y
C)15 × 10⁹ y
D)20 × 10⁹ y
E)25 × 10⁹ y

Question 23

One star has a surface temperature of 6000 K and another has a surface temperature of 7000 K. If the two stars have the same absolute luminosity, and if the radius of the 6000 K star is R₆ and the radius of the 7000 K star is R₇, what is the ratio R₆/ R₇?

A)0.7
B)1.2
C)1.4
D)1.6
E)1.9

Question 24

If a spherical galaxy of diameter 100,000 ly contained enough mass to be a black hole, what would be its mass?

A)200 x 10⁹ kg
B)400 x 10⁹ kg
C)6.9 x 10²³ kg
D)3.2 x 10⁴⁷ kg
E)6.4 x 10⁴⁷ kg

Question 25

About 1 μs after the Big Bang, the temperature of the universe was about 10¹³ K. What energy (in eV) does this correspond to?

A)1 neV
B)1 keV
C)1 MeV
D)1 GeV
E)1 TeV

Question 26

It can be shown that the approximate age of the universe is 1/H, where H is the Hubble constant. Taking H = 20 km/s/Mly, estimate the age of the universe, in years.

A)1500 years
B)15 thousand years
C)15 million years
D)15 billion years
E)15 trillion years

Question 27

Estimate the observed wavelength for the 656 nm line in the spectrum of a star which is 100 million light-years from us.

A)653 nm
B)659 nm
C)661 nm
D)677 nm
E)692 nm

Question 28

Two identical stars are located at different distances, one star at 2.0 pc and the other at 6.0 pc. How many times greater is the apparent brightness of the nearer star when compared to the more distant one?

A)1.7 times
B)3.0 times
C)9.0 times
D)18 times
E)27 times

Question 29

The Earth's orbit has a mean radius of 1.5 × 10⁸ km. Over a six-month period, the apparent position of a particular star varies by 0.00014° due to parallax. How distant is the star, in ly? (1 ly = 9.46 × 10¹⁵ m)

A)0.13 ly
B)1.3 ly
C)13 ly
D)130 ly
E)1300 ly

Question 30

The apparent brightness of a star is 1.0 × 10^-12 W/m² and the peak wavelength is 600 nm. Estimate its distance from us.

A)0.090 pc
B)0.90 pc
C)9.0 pc
D)90 pc
E)900 pc

Question 31

If a sphere of material with average density 1000 kg/m³ were made large enough to reach the Schwarzschild radius, what would be its mass?

A)4.3 x 10⁸ m
B)4.0 x 10¹¹m
C)1.3 x 10²⁸ kg
D)2.7 x 10³⁸ kg
E)3.4 x 10⁴⁵ kg

Question 32

What is the parallax angle for Proxima Centauri, which is Earth's nearest star at 4.3 ly?

A)1.2 × 10^-14 degrees
B)2.1 × 10^-4 degrees
C)1.2 × 10^-7 degrees
D)2.1 × 10^-7 degrees
E)2.1 × 10^-14 degrees

Question 33

If a galaxy is moving away from us at 1.0% of the speed of light, how far away is it from us?

A)14 ly
B)140 ly
C)140 thousand ly
D)140 million ly
E)140 billion ly

Question 34

The Sun has apparent brightness at Earth (1.5 × 10⁸ km away) of B. What would be the apparent brightness of the Sun at Pluto, which is 6.0 × 10⁹ km from the Sun?

A)0.50 B
B)0.25 B
C)0.063 B
D)0.025 B
E)0.00063 B

Question 35

A star has absolute luminosity equal to that of the Sun (1.5 × 10⁸ km from the Earth) but is 10 pc away from the Earth. By what factor will it appear dimmer than the Sun?

A)2 × 10^-9
B)2 × 10^-11
C)2 × 10^-13
D)2 × 10^-15
E)2 × 10^-17

Question 36

The Earth's orbit has a mean radius of 1.5 × 10⁸ km. Over a six-month period, the apparent position of a particular star varies by 0.00014° due to parallax. How distant is the star, in km?

A)1.2 × 10¹¹ km
B)1.2 × 10¹⁴ km
C)1.2 × 10¹⁷ km
D)1.2 × 10²⁰ km
E)1.2 × 10²³ km